Segmented Bowl – # 4 Cutting Individual Segment Blanks, Making Plywood

Next is to rip the blanks into six pieces that form the blanks for the actual segments.  This starts by ripping the piece along the glue joint between the two cherry pieces on the table saw.  The red arrow in the bottom photo points to that joint.

Using the chop saw with a stop block for accuracy each half of the just cut blank (red arrow) gets cut into three pieces.  Just to the left of the blank is a pencil.  I use its eraser end to hold the blank down when the cut is being made in case somethings wrong my fingers are away from the blade.  The three cut pieces are shown toward the bottom of the photo in front of the uncut blank. Twelve of these individual blocks will make up each of the four rings used in the bowl’s major feature band.

Using the pencil as a safety device to keep my fingers away from the blade turned out to be a really, really good idea since when I was cutting the 5th block somehow the piece got awry getting caught up in the blade, demolishing it and ripping the pencil out of my hand.  Fortunately, all that happened to me was a short-term slight numbness in my hand from the force when the pencil got yanked away.  It all happened so fast that I don’t really know what went wrong but my best guess is the shim used on the right side of the blade to level the blank somehow caused the piece to pinch against the blade causing the catch.  The result is the larger piece got thrown out to the right a few feet with the small piece nowhere to be seen.  I did find it about 15’ away from the saw when I was sweeping up at the end of the day.  After removing the shim there was no problem in making the rest of the cuts although I did have to reset the stop block as the impact moved it. 

Here is what all 59 of the pieces look like ready for their ends to be cut at 15 degrees so 12 of them per ring can be assembled into the four needed rings.  At this point the segment blanks are set aside while some other parts of the bowl are worked on.

The base of the bowl is next.  A typical ring is made up of twelve segments open in the center like the drawing on the top left.  That does not work for the bottom layer since a solid bottom is needed.  One could use a solid piece of wood here but due to differential expansion and contraction caused by changes in humidity either the rings or the base would probably crack and that’s not acceptable.  Using a ring like the one on the top right is possible but does come with its own problems.  I have used a hybrid ring with a small 1” diameter tapered plug in the center and that helps but don’t like the aesthetics.  I have gotten around that problem with the solution shown in the bottom drawing.  The blue piece is a three-layer shop made piece of oak plywood 3/16” thick.  It floats in a slot made in the bottom layer and capped with the next layer up.  The left half of the bottom drawing is before turning and the right side is a rough idea of what the finished turning will look like.

When selecting a piece of oak for the plywood I wanted a stable piece so sorted through my shorts until I found a piece that did not have the growth rings running parallel to the long face.  My first preference would be one where the growth rings are 90 degrees to the long face or quarter sawn.  The bottom photo is of the one selected and since only the left two thirds of the left side of the piece will be used most of the rings are at a 45 degree or so angle to the face which should give me a pretty stable finished part.

The plywood will be made from three layers each 1/16” thick.  To make the layers the selected piece of oak has a thin slice just over 1/16” cut off using the bandsaw.  The setup is shown in the two photos below.

To remove the bandsaw blade cut roughness out the thin piece gets run through the thickness sander.  To support the piece as it’s run through the sander a ¼” thick carrier is used.  The top photo shows it ready to go through the sander.  I have marked the bandsawn surface with a pencil to gauge when it’s smooth as it’s run though the sander.  The bottom photo is a dial caliper showing the piece being just a tiny bit under 1/16” thick.

After cutting three layers of the oak to size they are glued up with the middle layer’s grain running 90 degrees to the top and bottom layers.  The top photo shows how they will get stacked and the bottom photo is the setup for gluing.

Once the layers are glued and aligned, they get taped to a backer board that has a melamine covering the glue will not stick to.  This assembly is set in the bench vice, another backer board added and the vice tightened.  Last is to add two C-clamps to securely clamp the top edge.  The piece is left overnight for the glue to cure. 

With the floating insert glue curing I can select material to make the bottom two segmented layers.  The first step is to refer to a spreadsheet (below) that has all the information about the segments size for each ring.  The blue numbers (radius, width and thickness) are those that I entered and the rest are calculated based on them.

In the left drawing below the green is the finished profile of the bowl and the grey areas are a buffer for small changes in the design as it gets turned on the lathe.  The right side shows a cross section and sizes of each of the individual segments that make up the layers.  The dimensions that go into the spreadsheet come from this drawing.

Next Up – Making and Mounting the Bottom Layer